In the field of mobile phones, new models of multifunction are being developed one after another. Multifunction is a requirement of the time. On the other hand, extending a continuous operation time without charging has been a fundamental requirement. In this circumstance, various power-saving measures are proposed, some of them being conducted.
In a mobile phone, power is consumed not only during a phone call but also in a standby mode. The power-consuming part of a mobile phone includes a control unit (CPU) for controlling the entire mobile phone, a radio communication unit for performing transmission/reception, and a display unit.
For example, in a folding mobile phone, in which the display unit cannot be seen when folded, the display unit is not driven so as to save power when the mobile phone is folded and is in a standby mode. Since the display unit cannot be seen when the mobile phone is folded, power-saving measures in which the display unit is not driven is very effective and practical.
However, in an ordinal mobile phone which cannot be folded, time and the amount of remaining battery should be displayed even in a non-operating standby mode. Therefore, most of commercially available mobile phones are configured such that time and the amount of remaining battery are displayed.
In response to such requirements, mobile phones including an STN-type liquid crystal display unit, which have the following function, have been proposed. That is, the entire liquid crystal display unit is not driven and only time and the amount of remaining battery can be partially displayed in a non-operating standby mode.
On the other hand, the display unit of mobile phones is expected to shift from an STN-type liquid display to a TFT-LCD in accordance with requirements of colorization, high-resolution, and moving image. Since power consumption will increase in accordance with colorization, high-definition, and adoption of a TFT-LCD, requirement for power saving will further increase. However, the TFT-LCD uses a different driving technique from that for the STN-type liquid crystal display. Thus, the above-described power-saving measures for the STN-type liquid crystal display unit cannot be applied to the TFT-LCD. Therefore, under present circumstances, only a method as disclosed in Japanese Unexamined Patent Application Publication No. 10-65598, in which the entire display unit is not at all driven, can be applied in order to save power in the TFT-LCD. In this method, however, time and the amount of remaining battery cannot be displayed in a non-operating standby mode.
Accordingly, the present invention provides a power-saving driving method for a TFT-LCD display device in which required information can be displayed while reducing power consumption in a TFT-LCD in a non-operating standby mode in a mobile phone or the like including a TFT-LCD.